Recently thin display apparatuses using self-luminous devices such as an organic EL device and an FED have actively been developed. It is known that the self-luminous devices have characteristics such that the luminance of the device is proportional to the current density of the current passing through the device. It is also known that the characteristics of the devices, especially the characteristics of the applied voltage-current fluctuate so that a drive circuit using a constant current source is preferably used for the devices. However, it is difficult to construct the constant current source in reality and hence a constant current drive circuit is arranged using a constant voltage source. For this case, a proposed method is to provide means for detecting a current passing through a device and control the current detected by the means to be consistent.
FIG. 33 illustrates an organic EL display 101 which is an example of luminance correction using the above-identified current detection means, disclosed in Japanese Laid-Open Patent Publication No. 2000-187467 (Tokukai 2000-187467; published on Jul. 4, 2000). This display 101 is a passive drive display, including an organic EL panel 102 which is arranged such that a plurality of cathodes c0 to cn and a plurality of anodes s0 to sm, which are intersecting with each other, partition a display area in a matrix manner, and an organic EL device 103 is provided in each portion of the partitioned display area.
Outside of or being integrated into the organic EL panel 102, a cathode drive circuit 104 for driving the cathodes c0 to cn, anode drive circuits pg0 to pgm for driving each of the anodes s0 to sm individually, and current detection circuits is0 to ism for detecting each output current from the anode drive circuits pg0 to pgm. The current detection circuits is0 to ism (collectively termed is) detects a current value so as to supply the same to a control device 105, and in accordance with the detected current value, a luminous period or a luminous current, which is matched with the display information of each portion of the display area, is controlled.
The current detection circuit is is, as shown in FIG. 34, arranged such that a current detection resistor r1 is inserted in series with a line connected to one of the anodes s0 to sm, and an inter-terminal voltage of the current detection resistor r1 is detected in an A/D conversion circuit 106 so as to be output.
FIG. 35 illustrates an organic EL display 111 which is another example of luminance correction using the above-identified current detection means, disclosed in Japanese Laid-Open Patent Publication No. 10-254410/1998 (Tokukaihei 10-254410; published on Sep. 25, 1998). This display 111 is an active drive display, arranged such that the sum-total of the current values passing through all pixels is regulated by: (i) driving all organic EL devices of a display panel 112, by a controller 113, at a constant voltage via a scanning circuit 114 and a power source circuit 115; (ii) storing a current value, which is measured using. a method described below, in a current value memory 116; (iii) processing the stored data and display data in an arithmetic circuit 118, the latter data being supplied from the outside via an A/D conversion circuit 117; and (iv) supplying the display data obtained in (iii) to each pixel via a frame memory 119 and a write circuit 120.
In the case of this active drive, each pixel 121 of the display panel 112 is arranged as illustrated in FIG. 36. That is, the pixel 121 includes: a TFT 122 for capturing the display data; a capacitor 123 for storing the captured display data; an organic EL device 124, a TFT 125 for driving the organic EL device 124 in accordance with an output voltage of the capacitor 123; and a current detector 126 for detecting a current passing through the organic EL device 124.
The TFT 122 is brought into conduction by selecting a scanning signal line, and a voltage of a data signal line is stored in the capacitor 123. Using the voltage stored in the capacitor 123, a TFT 125 is controlled even when the TFT 122 is out of conduction so that an amount of the current passing through the organic EL device 124 is regulated. So in this case the above-identified regulation of the sum-total of the current values is done by: providing the current detector 126 between the TFT 125 and the organic EL device 124; converting the output of the current detector 126 into digital data in an A/D conversion circuit 127; and storing the data in the current value memory 116.
In the above-identified prior art, a passive drive display apparatus such as the display 101 disclosed in Japanese Laid-Open Patent Publication No. 2000-187467 successively selects the cathodes c0 to cn so that measuring currents passing through the anodes s0 to sm is to measure the current of the organic EL device 103 which is intersected with the selected cathode. In the meantime, an active drive display apparatus such as the organic EL display 111 disclosed in Japanese Laid-Open Patent Publication No. 10-254410/1998 is arranged so that, as described above, even if the scanning signal line is not selected, the TFT 125 is controlled using the voltage of the capacitor 123 so that a current passes through the organic EL device 124. Thus the measurement of the current of each organic EL device 124 can be carried out only on a device-by-device basis so that it is not possible to effectively measure the current passing through organic EL device(s) by simply measuring the current of each signal line, from outside of the display area as in the case of the passive drive. Moreover, it is also not possible to enlarge the area of each organic EL device 124, i.e. to increase the numerical aperture.